Silsilat al-Ahadith al-Sahihah

Salim bin Amir says that Sayyiduna Muawiyah (may Allah be pleased with him) had a treaty with the Romans. Sayyiduna Muawiyah (may Allah be pleased with him) was traveling in their land until the period of the treaty ended. He (taking advantage of the opportunity) attacked them. A man, who was riding an animal or a horse, said: "Allahu Akbar! Fulfill the treaty, do not break the treaty." He was Sayyiduna Amr bin Abasah Salami (may Allah be pleased with him). Sayyiduna Amir Muawiyah (may Allah be pleased with him) said to him: "What are you saying?" Amr said: "I heard the Messenger of Allah (peace and blessings be upon him) say: 'If a man has made a treaty with a people, he should neither break it nor strengthen it until the period ends, or (if he fears treachery from them) he should inform them of the termination of the treaty, so that both sides are equal in breaking the treaty.'"